Many systems are known in the prior art for testing currency notes to determine the genuineness thereof and to discriminate between notes of different denominations. Most of these devices involve reading indicia printed on a face of the note and comparing it with stored data. Some of the devices involve a rough measurement of a dimension of the note in the direction of travel thereof through the device.
A few devices of the prior art make a determination of the dimension of a note in a direction transverse to the direction of travel thereof. For example, Pauli et al U.S. Pat. No. 4,435,834 discloses an arrangement in which the note passes through the space between an illuminating means and a row of photodiodes. The number of darkened photodiodes is counted and divided by the number of diodes per unit width to obtain a measure of width which is compared with maximum and minimum values.
Favre U.S. Pat. No. 4,298,807 discloses an arrangement in which the document passes by an array of sixty photodiodes corresponding to the maximum width of the document to be inspected. These photodiodes are arranged in groups of four for analog multiplexing. The outputs of the multiplexing circuit are applied to analog to digital converters and averaging circuits and to a common comparator circuit to give information as to the dimension of a note.
While the systems just described afford a rough indication of the width of a document being inspected, the measurement afforded thereby is not as accurate as is desirable in many instances. For example, in certain countries respective denominations of currency are differentiated by width. Known systems do not afford as accurate a width measurement as is necessary effectively to discriminate between notes of different denominations.